Industrial process control systems are used to monitor and control industrial processes used to produce or transfer fluids or the like. In such systems, it is typically important to measure process variables such as temperatures, pressures, flow rates, levels, and others. Process control transmitters measure such process variables and transmit information related to the measured process variable back to a central location such as a central control room.
One type of process variable transmitter is a pressure transmitter which measures process fluid pressure and provides an output related to the measured pressure. This output may be a pressure, a flow rate, a level of a process fluid, or other process variable that can be derived from the measured pressure. The pressure transmitter is configured to transmit information related to the measured pressure back to the central control room. Transmission is typically provided over a two-wire process control loop, however, other communication techniques are sometimes used.
One particularly challenging environment for pressure measurement is applications which have very high working pressure. One such application is the subsea environment. In such applications, the static pressure to which the process equipment is exposed can be quite high. Moreover, the process fluid can corrode many known metals. For example, some subsea applications are now being considered that require a 20,000 psi maximum working pressure (MWP). Such considerations typically require specialized high-performance, high-cost exotic materials in order to provide a robust structure. Examples of such high-performance, high-cost corrosion-resistant alloys include Hastelloy® C-276 available from Haynes International, Inc. of Kokomo, Ind. or Inconel® 625 available from Special Metals Corporation of New Hartford, N.Y. While the selection of such exotic alloys can allow process variable transmitters to operate in such hostile environments, they do typically increase the cost of the overall structure.